Powered work-clamping devices



g- 1967 c. w. TRIDGELL POWERED WORK-CLAMPING DEVICES 2 Sheets-Sheet 1 Filed April 6, 1964 Aug. 1 1957 c. w. TRIDGELL POWERED WORK-CLAMPING DEVICES Filed April 1964 2 Sheets-Sheet 3 United States Patent 3,336,022 POWERED WORK-CLAMPING DEVICES Cyril William Tridgell, Hemel Hampstead, England, as-

signor to Power Jacks Limited, a corporation of Great Britain Filed Apr. 6, 1964, Ser. No. 357,511 Claims priority, application Great Britain, Apr. 4, 1963, 13,340/ 63 2 Claims. (Cl. 269-32) This invention relates to powered work-clamping devices, such as are now frequently used on machine tools to hold a workpiece on to a table or jig while some mechanical operation, such as milling, drilling or grinding, is effected.

The invention relates particularly to powered workclamping devices of the kind, hereinafter termed the kind referred to, in which the clamp is actuated by a fluid under pressure and has, in addition to the clamping movement, a work-clearing movement, such as a swinging movement, in a direction different from the clamping movement, both movements being actuated from the same source of fluid pressure.

A clamp of the kind referred to is the subject of my co-pending application for British Patent No. 40,048/ 60.

One of the problems associated with such work-clamping devices, is to arrange for the two movements to operate in a particular sequence so that for clamping it is ensured that the clamp shall move fully from its workclearance position into its extended work-clamping position before the clamping movement commences; and equally for unclamping so that the clamp is fully lifted or otherwise retracted before the work-clearing movement of the clamp commences. This can be, and is, easily effected, where the movements are spring-loaded for return, by differential spring loading of such movements and by biasing the clamping movement by a control valve. Such bias loaded valve however introduces further problems in that, since time saving is an important factor, and since the work-clearing movement has some inherent inertia, the quicker the work-clearing movement the heavier must be the control valve bias loading in order to prevent premature clamping movement being caused by the pressures necessary to provide the acceleration against such inertia. Any bias loading of the valve, however, as at present provided, is in efliect a bias loading of the ram chamber pressure, as such loading is subtracted from the available clamping pressure so that any such arrangement is necessarily a compromise to set off increased speed of movement against loss of clamping power.

The object of the present invention is to provide a powered Work-clamping device having valve biased control with its known simplicity and advantages, but without the disadvantages aforesaid.

According to the invention a powered work-clamping device of the kind referred to having a hydraulic bias control valve is characterised by means responsive to the working movement of the clamp, so arranged as to remove the bias loading of the ram chamber pressure during an initial clamping movement and to restore the bias pressure loading during a final unclamping movement, whereby the full hydraulic pressure in the system is available for clamping without dilferential loss from such loading.

In the accompanying drawings:

FIG. 1 is a side elevation, and

FIG. 2 is a plan of one example of a powered workclamping device made in accordance with the present invention.

FIG. 3 is a section on line 33 of FIG. 2.

FIG. 4 is a section on line 44 of FIG. 1.

FIG. 5 is a fragmentary section on line 55 of FIG. 4.

As shown in the drawings the powered work-clamping device comprises a base 10 having a pair of lugs 11 and 12 by which it is adapted to be bolted to a work table, the base being formed with upstanding bosses 13 and 14. In the boss 13 is rotatably mounted a column 15 with head 15a located in a recess in the under side of the base. On the upper end of this column is pivotally mounted at 16 a clamping lever 17 fitted with a return spring 18 and having at one end an adjustable and renewable clamping anvil 19. Relatively inclined to such clamping lever the column 15 is formed with a notch 20 (see in FIGS. 3 and 4) complementary to a bevelled end of a plunger 21, with flats 21a to prevent rotation, the plunger having a return spring 22 held by a spring ring 23. A return torque spring 25 is housed in the boss 13 around the column and has one end located at 25a in such boss and the other end similarly located in a cover ring 26 adapted to be secured to the column by a socket-headed screw 27 and complementary locating socket 27a in the side of the column.

In the boss 14 is secured a spring cover 28 enclosing concentric return springs 29, 30 both engaging a common collar 31 abutting against a shoulder of a rain piston 32 the upper end 32a of which extends through such cover to engage the rear end of the clamping lever 17. The ram piston 32 is recessed at its lower end to carry a bias control valve 33 loaded by a spring 34 and retained by a spring ring 35. The valve 33 has a conical nose portion 33a adapted to seat as shown in FIG. 1 to close the end of a passage 36 communicating with the hydraulic space behind the plunger 21. A junction nipple 37 enables a. hydraulic power line to be connected to such hydraulic space. A pressure release valve 38 with loading spring 39 is located in the bias control valve 33 and a release passage 40 therefrom leads through the nose of the valve 33.

With the valve 33 normally seated as shown in FIG. 3

a clearance distance X exists between the retaining ring 35 and a shoulder at the lower end of the valve 33 surrounding the conical nose of such valve.

In operation, with no fluid pressure present, the clamping ram 32 and valve 33 will be in the position shown in FIG. 3 but for convenience the clamping arm 17 and swinging ram 21 are shown moved into position by an initial hydraulic pressure insufficient to open the valve 33 in readiness for work clamping. In order to swing the clamping lever from its work-clearing position to the work clamping position as quickly as possible the valve 33 must be loaded for example to 1000 p.s.i. for use with an available fluid pressure up to 12.00 p.s.i. During movement of the ram 21 into the ready position for clamping, the pressures in the ram chamber and in the passage 36 Will not normally reach the figure of 1000 p.s.i. but as soon as movement of this ram ceases the pressure will rise almost instantly to above that figure so as to raise the control valve 33 and admit fluid pressure to the chamber for the clamping action of the ram 32. Such pressure however is only the differential pressure so long as the valve 33 is able to reach its seating and on the figures above given cannot exceed 200 p.s.i. This is suflicient however to move the ram 32 against the combined resistance of the springs 29 and 30' so that upward movement of the ram commences. As soon as the ring 35 engages the shoulder of the valve 33- it lifts the valve off its seating and thereafter the full hydraulic pressure enters the ram chamber below the ram 32 through the passage 36 and therefore full clamping pressure is available from the rain 32.

To release the clamp the hydraulic pressure to the passage 36 is cut off and said passage vented and thereafter the pressure in the chamber below the ram 32 is determined momentarily by the springs 29 and 30 above the ram, which pressure in the passage 36 is also present behind the ram 21 and is suificient to overcome its return spring 22 and therefore to hold the ram 21 and lever 17 from moving to the work-clearing position. When the valve 33 reaches its seating the hydraulic pressure in the passage 36 drops rapidly allowing the spring 22 to withdraw the ram and the torque spring to swing the lever 17 clear of the work.

After the valve 33 closes onto its seat hydraulic fluid still below the ram is allowed to leak .past the valve 33 and escape past the valve 38 and through the bleed hole 40 into the still vented passage 36 allowing the piston 32 to finish its downward movement and re-establish the clearance X. The action of the return spring 18 for the clamp and the use of the adjustable anvil 19 are so obvious as to require no explanation.

The swinging action of the lever is reversible so as to move clockwise or anti-clockwise and this change may be eifected by releasing the screw 27, turning the cover ring 26 until the torque spring is loaded in the other direction and then re-fixing the screw. Also the plunger 21 requires turning on its axis through 180 degrees complementary to the change of direction of the slot 20 in the column.

The invention is not limited to the example above-described in which the bias loading of the valve is itself effectively removed by moving the valve beyond the effective range of movement of the loading spring. For instance, the movement of the ram could operate to open and close a by-pass to the ram cylinder from the passage 36.

What I claim is:

1. A fluid-actuated swing clamp comprising, a pivotally mounted clamping arm, a ram for moving the arm to a work-clamping position, said ram having a pressure chamber, a hydraulic bias control valve for the hydraulic fluid pressure for the ram, means responsive to the working movement of the arm to remove the bias loading of the ram pressure chamber during an initial clamping movement of the arm, said means being eifective to restore the bias pressure loading during a final unclamping movement of the arm, whereby full hydraulic pressure in the system is available for clamping without differential loss from such unloading, said control valve being movable relative to its seat with the movement of the ram being such as to be unseated and reseated respectively with the initial or engaging movement and final return movement of the ram, the control valve being normally mounted on and coaxial with the ram with limited biasloaded relative movement, a leak-away by-pass in the control valve fitted with a non-return valve and releasing residual pressure in the ram cylinder after the bias-valve has been reseated.

2. A fluid-actuated swing clamp comprising, a base, a column rotatively mounted in the base, a clamp arm pivotally mounted on the column, a swing ram arranged to turn the column from a clearance position for the clamp to working position, spring means for returning the column with the clamp to the clearance position, a clamping ram adapted to engage the clamp arm at its rear end to provide clamping pressure on work engaged by the arm, return spring means for the clamping arm, a connecting passage permanently connecting the pressure chambers of the two rams, a bias valve of substantially smaller seating area than the swing ram carried by the clamping ram and adapted to close the connecting passage when the clamping ram is in its returned position, spring means for loading said bias valve, and means on the clamping ram engageable with the valve to withdraw the valve out of reach of the connecting passage after a small initial movement of the clamping ram, the spring for the valve being of such strength as to provide resistance to valve opening less than the maximum available pressure but greater than that required to overcome the swing return springs, and the swing inertia of the clamp and its swing ram for movement from the clearance position to the working position.

References Cited UNITED STATES PATENTS 2,335,917 12/1943 Cuthbert 914l2 2,616,259 11/1952 Quintilian 91-412 2,908,205 10/1959 Furman 269134 2,967,464- 1/1961 Marmillon 26930 3,173,673 3/ 1965 Northern 26932 HAROLD D. \NHITEHEAD, Primary Examiner. 

1. A FLUID-ACTUATED SWING CLAMP COMPRISING, A PIVOTALLY MOUNTED CLAMPING ARM, A RAM FOR MOVING THE ARM TO A WORK-CLAMPING POSITION, SAID RAM HAVING A PRESSURE CHAMBER, A HYDRAULIC BIAS CONTROL VALVE FOR THE HYDRAULIC FLUID PRESSURE FOR THE RAM, MEANS RESPONSIVE TO THE WORKING MOVEMENT OF THE ARM TO REMOVE THE BIAS LOADING OF THE RAM PRESSURE CHAMBER DURING AN INITIAL CLAMPING MOVEMENT OF THE ARM, SAID MEANS BEING EFFECTIVE TO RESTORE THE BIAS PRESSURE LOADING DURING A FINAL UNCLAMPING MOVEMENT OF THE ARM, WHEREBY FULL HYDRAULIC PRESSURE IN THE SYSTEM IS AVAILABLE FOR CLAMPING WITHOUT DIFFERENTIAL LOSS FROM SUCH UNLOADING, SAID CONTROL VALVE BEING MOVABLE RELATIVE TO ITS SEAT WITH THE MOVEMENT OF THE RAM BEING SUCH AS TO BE UNSEATED AND RESEATED RESPECTIVELY WITH THE INITIAL OR ENGAGING MOVEMENT AND FINAL RETURN MOVEMENT OF THE RAM, THE CONTROL VALVE BEING NORMALLY MOUNTED ON AND COAXIAL WITH THE RAM WITH LIMITED BIASLOADED RELATIVE MOVEMENT, A LEAK-AWAY BY-PASS IN THE CONTROL VALVE FITTED WITH A NON-RETURN VALVE AND RELEASING RESIDUAL PRESSURE IN THE RAM CYLINDER AFTER THE BIAS-VALVE HAS BEEN RESEATED. 